C5 Chemical Changes Flashcards
A salt
Compound formed during a neutralisation reaction when some or all hydrogen ions in an acid are replaced with metal ions or ammonium ions
Neutralisation reaction
When an acid and a base are added together they cancel each other out and form a neutral solution
How to make a salt by reacting a metal with an acid
Salt is formed by replacing hydrogen ions in the acid with metal ions or aluminum ions
The reaction between a metal and an acid
Metal + acid ——> salt + hydrogen
A salt formed between a metal and sulfuric acid or hydrochloric acid
Salt will be chloride if acid is hydrochloric acid
Salt will be sulphate if acid is sulphuric acid
Which species is oxidised and which is reduced
in a reaction
The species that loses electrons is oxidized
The species that gains electrons is reduced
The reaction between a metal oxide or metal hydroxide and an acid
Acid + metal oxide = corresponding salt + water
Why the reaction between a base and a dilute acid is a neutralisation reaction
If a base is added to an acidic solution the solution becomes less acidic and moves toward the middle of the pH scale
How alkalis are a subgroup of bases
An alkali is a water-soluble base
Bases which can be dissolved in water to furnish OH-ions
How to make a salt reacting a metal carbonate with a dilute acid
Dilute hydrochloric acid
Add powdered zinc carbonate to acid
Continue to add powder until excess amount
Filter mixture in beaker to remove excess zinc
What happens when ammonia react with acid
Formation of a salt of weak bases and strong acid
Balanced equation for neutralisation reaction
NaOH + HCl ————> NaCl + H2O
How to use universal indicator to classify as acidic or alkaline
Few drops of universal indicator solution is added to each substance at a time
The colour obtained is compared to pH chart to give pH of solution
pH scale
Measures how acidic or alkaline an object is
Lowest 0 highest 14
Pure water has pH 7
Alkali effect on solution
A base or an alkali takes up hydrogen ions
Example of alkali
Sodium hydroxide
Example of a neutral
Pure water
Example of a base
Copper oxide
Acidic chemical example
Hydrochloric acid
Relationship between alkalis and bases
Alkali is a base
A base that dissolves in water
Not all bases are alkali but all alkali is base
How the pH of a solution changes as acid or alkali is added
pH below 7 is acidic
pH above 7 is alkaline
Acid added = pH decreases
Alkali added = pH increases
Examples of strong acids
Hydrochloric acid (HCl)
Sulfuric acid (H2SO4)
Nitric acid (HNO3)
Examples of weak acids
Acetic acid
Citric acid
Carbonic acid
How an acid or alkali can be concentrated or dilute
By adding water to a concentrated acid or base, the solution is diluted
How an acid or alkali can be strong
A strong acid is one that’s nearly or completely ionised in water
How an acid or alkali can be weak
If it’s only partially ionised in water
How concentration of hydrogen ions relates to pH number
As concentration of hydrogen ions increase the pH decreases
Acid
A substance that produces hydrogen ions when dissolved in water
The lower the pH solution…
…the more acidic it is
The higher the pH solution…
…the more alkaline it is
Indicator
A dye that changes colour depending on whether it’s above or below a certain pH
Wide range indicator
Indicators which contain a mixture of dyes so gradually change colour over a broad range of pH
What are wide range indicators used for
Estimating the pH of a solution
Why is a pH probe more accurate than an indicator
When the probe is placed in solution you’re measuring the pH is given on a digital display as a numerical value
How does a pH probe work
Attached to a pH meter can be used to measure pH electronically
What substance do acids form in water
H+ ions
What substance do alkalis form in water
OH- ions
Base
Substance with pH greater than 7
Neutralisation
The reaction between acids and bases
Neutralisation reaction word equation
Acid + base ——–> salt + water
Neutralisation reaction symbol equation
H+(aq) + OH-(aq) ——> H2O(I)
What happens when an acid neutralises a base
The products are neutral (they have a pH of 7)
Use of titrations
Allow you to find out exactly how much acid is needed to neutralise a quantity of alkali
Titration experiment
Steps 1-3
Using a pipette and pipette filter add a set volume pf alkali to conical flask
Use funnel to fill a burette with some acid of known concentration - make sure to do this below eye level
Record initial volume of acid in burette
Titration experiment
4-6
Using burette add acid to alkali a bit at a time giving conical flask a regular swirl
Go slowly when you think the end-point is about to be reached
Indicator changes colour when all alkali is neutralised
Record final volume of acid in the burette and use it along with initial reading to calculate volume of acid used to neutralise alkali
In titration experiment why do you need to use funnel to fill burette with acid
You don’t want to be looking up if some acid spills over
How to increase accuracy of titration
You need several consistent readings
Repeat whole thing few times
Universal indicator
Used to measure pH of a solution because it can turn a variety of colours
Each colour indicates a narrow range of pH values
What is universal indicator made of
Mixture of different indicators changes from red to violet
During titration when will you see colour change
At the end-point
What colour is litmus indicator
Blue in alkali and red in acids
What colour is phenolphthalein indicator
Pink in alkalis and colourless in acids
What colour is methyl orange indicator
Yellow in alkalis and red in acids
Reactvitiy series
List of metals in order of their reactivity towards other substances
The reactvity series order
Top half
Potassium
Sodium
Lithium
Calcium
Magnesium
The reactvity series order
Bottom half
Carbon
Zinc
Iron
Hydrogen
Copper
How are metals reactivity determined by
How easily they lose electrons
How to tell the speed of a reaction
Rate of which bubbles of hydrogen are given off
How to investigate reactivity of metals
By measuring temperature change of the reaction with acid or water over a time period
Metal reacts with water word equation
Metal + water ——> metal hydroxide + hydrogen
Calcium hydroxide
Ca(OH)2
Calcium reacts with water symbol equation
Ca + 2H2O ———> Ca(OH)2 + H2
Name the metals which react with water
Potassium, sodium, lithium and calcium
Name the metals which don’t react with water
Zinc, iron, copper
Oxidation
Gain of oxygen
Reduction
Loss of oxygen
2Mg + O2 ——–> 2MgO
Which is oxidised
Magnsium is oxidised to make magnesium oxide
2CuO + C ——> 2Cu + CO2
Which is reduced
Copper oxide is reduced to copper
What do metals need to be extracted from their ores chemically by reduction
Carbon
How are the metals higher than carbon extracted by
Electrolysis (expensive)
How are the metals lower than carbon extracted by
Reduction using carbon
Why are metals above and below carbon extracted differently
Carbon can only take oxygen away from metals which are less reactive than carbon
How to extract very unreactive metals
They are in Earth’s form as the metal itself
Is the ionisation of a weak acid reversible reaction or irreversible
Reversible reaction
Equation of strong acid
HCl ———-> H+ + Cl-
Equation of weak acid
CH3COOH ——\ H+ + CH3COO-
-—–
How to increase rate of reaction of acid
If concentration of H+ ions is higher
pH of an acid or alkali
A measure of concentration of H+ ions in solution
What happens to concentration for every decrease of 1 on the pH
Concentration increases by a factor of 10
What us the general rule for pH
-x
Factor H+ ion concentration changes by = 10
Which pH is stronger when they have same concentration weak or strong acid
Weak acid has more pH than strong acid if same concentration
What does concentration measure
How much acid there is in a certain volume of water
Metal reacts with oxygen equation
Metal + oxygen → metal oxide
Displacement reaction
When a more reactive element displaces a less reactive element from a compound
Why a displacement reaction may occur
More reactive metal has stronger tendency to lose electrons and form positive ions than less reactive metal
Example of displacement reactions using an ionic equation
Zn + CuSP4 ——> ZnSO4
How to use reactivity series to determine whether a reaction between a metal and different metal salt would happen or not
A metal will displace another metal from its salt solution if more reactive than the metal in the salt
How is carbon used to extract from an ore
Heating the metal oxide in the presence of the carbon
How is hydrogen used to extract from an ore
By reacting hydrogen directly with iron ore, iron and water are produced in place of iron and CO2
How are metals extracted
Electrolysis
Ionic equation for reaction between an acid and alkali
H+ + OH- ———-> H2O
Why are gold and silver found naturally as elements in Earth’s crust
Unreactive